(1) Field of the Invention
This invention relates to an anti-reflective coating formed on the bottom of a photoresist layer and more particularly to the deposition of a silicon nitride film having a low index of refraction, 1.9, over a silicon nitride film having a higher index of refraction, 2.1, to form the anti-reflective coating.
(2) Description of the Related Art
U.S. Pat. No. 5,378,659 to Roman et al. describes the use of a silicon-rich silicon nitride layer, having an absorptive index greater than 0.25, as an anti-reflective coating for use in photolithographic processing.
U.S. Pat. No. 5,441,914 to Taft et al. describes using a thin silicon layer between a patterned tungsten silicide layer and an overlying patterned silicon nitride anti-reflective layer to prevent delamination of the anti-reflective layer.
U.S. Pat. No. 5,216,542 to Szczyrbowski et al. describes a five layer system to provide an effective anti-reflective effect.
U.S. Pat. No. 5,126,289 to Ziger describes the use of an organic material which is highly absorptive of deep ultra violet actinic light to provide anti-reflection effects as well as surface planarization.
U.S. Pat. No. 5,449,639 to Wei et al. describes a method of metal etching using a disposable metal anti-reflective coating.
The anti-reflective coating described in this Patent Application uses a second silicon nitride layer, having a low silicon to nitrogen ratio and a relatively low index of refraction, formed over a first silicon nitride layer, having a high silicon to nitrogen ratio and a relatively high index of refraction, to provide an effective anti-reflective coating.